add: util method for generating date

tests/date-formatter-test.js

@@ -0,0 +1,45 @@
+/**
+ * @fileoverview Unit test for browser/lib/date-formatter.js
+ */
+const test = require('ava')
+const { getLastUpdated } = require('browser/lib/date-formatter')
+
+/**
+ * @description Get local Date insance.
+ * @param {numbr} year
+ * @param {number} month
+ * @param {number} day
+ * @param {number} hour
+ * @param {number} minute
+ * @param {number} second
+ * @return {Date}
+ */
+function generateLocalDate(year, month, day, hour, minute, second) {
+  const date = new Date()
+  date.setDate(day)
+  date.setFullYear(year)
+  date.setHours(hour)
+  date.setMinutes(minute)
+  date.setMonth(month - 1)
+  date.setSeconds(second)
+  return date
+}
+
+test(t => {
+  const testCases = [
+    [generateLocalDate(2016, 9, 9, 12, 0, 0), 'Sep.9, 2016 12:00'],
+    [generateLocalDate(2016, 9, 9, 2, 0, 0), 'Sep.9, 2016 02:00'],
+    [generateLocalDate(2016, 5, 9, 2, 1, 0), 'May9, 2016 02:01'],
+  ]
+
+  for (let testCase of testCases) {
+    t.is(testCase[1], getLastUpdated(testCase[0]))
+  }
+})
+
+test(t => {
+  t.throws(
+    () => getLastUpdated('invalid argument'),
+    'Invalid argument. Only instance of Date Object'
+  )
+})